Data storage device erasing multiple adjacent data tracks to recover from inter-track interference

ABSTRACT

A data storage device is disclosed comprising a disk comprising a plurality of data tracks, and a head actuated over the disk. A retry operation for a target data track is performed by positioning the head at a first radial location and first erasing at least part of a first data track adjacent the target data track. After the first erasing, the target data track is first read to first recover target data recorded in the target data track. When the first recovery fails, the head is positioned at a second radial location and more of the first data track is second erased. After the second erasing, the target data track is second read to second recover the target data recorded in the target data track.

BACKGROUND

Data storage devices such as disk drives comprise a disk and a headconnected to a distal end of an actuator arm which is rotated about apivot by a voice coil motor (VCM) to position the head radially over thedisk. The disk comprises a plurality of radially spaced, concentrictracks for recording user data sectors and servo sectors. The servosectors comprise head positioning information (e.g., a track address)which is read by the head and processed by a servo control system tocontrol the actuator arm as it seeks from track to track.

FIG. 1 shows a prior art disk format 2 as comprising a number of servotracks 4 defined by servo sectors 6 ₀-6 _(N) recorded around thecircumference of each servo track. Each servo sector 6 _(i) comprises apreamble 8 for storing a periodic pattern, which allows proper gainadjustment and timing synchronization of the read signal, and a syncmark 10 for storing a special pattern used to symbol synchronize to aservo data field 12. The servo data field 12 stores coarse headpositioning information, such as a servo track address, used to positionthe head over a target data track during a seek operation. Each servosector 6 _(i) further comprises groups of servo bursts 14 (e.g., N and Qservo bursts), which are recorded with a predetermined phase relative toone another and relative to the servo track centerlines. The phase basedservo bursts 14 provide fine head position information used forcenterline tracking while accessing a data track during write/readoperations. A position error signal (PES) is generated by reading theservo bursts 14, wherein the PES represents a measured position of thehead relative to a centerline of a target servo track. A servocontroller processes the PES to generate a control signal applied to ahead actuator (e.g., a voice coil motor) in order to actuate the headradially over the disk in a direction that reduces the PES.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art disk format comprising a plurality of servotracks defined by servo sectors.

FIG. 2A shows a data storage device in the form of a disk driveaccording to an embodiment comprising a head actuated over a diskcomprising a plurality of data tracks.

FIG. 2B is a flow diagram according to an embodiment wherein during aretry operation for a target data track an adjacent data track isincrementally erased toward the target data track.

FIGS. 3A and 3B illustrate a prior art technique for performing a retryoperation by erasing an adjacent data track one time which may erasepart of the target data track.

FIGS. 4A-4F illustrate an embodiment wherein an adjacent data track ispartially and incrementally erased toward a target data track during theretry operation so as not to erase part of the target data track.

FIG. 5 is a flow diagram according to an embodiment wherein after eachincremental erase of the adjacent data track the target data track isread multiple times using different radial offsets during the retryoperation.

FIG. 6 illustrates an embodiment wherein the read element is positionedat different radial offsets when reading the target data track duringthe retry operation.

FIG. 7 illustrates an embodiment wherein an AC erase signal used toerase the adjacent data track comprises a frequency higher than thefrequency of the target data recorded in the target data track.

DETAILED DESCRIPTION

FIG. 2A shows a data storage device in the form of a disk driveaccording to an embodiment comprising a disk 16 comprising a pluralityof data tracks 18, and a head 20 actuated over the disk 16. The diskdrive further comprises control circuitry 22 configured to execute theflow diagram of FIG. 2B, wherein when a retry operation for a targetdata track is needed (block 24), the head is positioned at a firstradial location (block 26) and at least part of a first data trackadjacent the target data track is first erased (block 28). After thefirst erasing, the target data track is first read to first recovertarget data recorded in the target data track (block 30). When the firstrecovery fails (block 32), the head is positioned at a second radiallocation (block 34) and more of the first data track is second erased(block 36). After the second erasing, the target data track is secondread to second recover the target data recorded in the target data track(block 38).

In the embodiment of FIG. 2A, a plurality of servo tracks are defined byembedded servo sectors 40 ₀-40 _(N), wherein the data tracks 18 aredefined relative to the servo tracks at the same or different radialdensity. The control circuitry 22 processes a read signal 42 emanatingfrom the head 20 to demodulate the servo sectors and generate a positionerror signal (PES) representing an error between the actual position ofthe head and a target position relative to a target track. The controlcircuitry 22 filters the PES using a suitable compensation filter togenerate a control signal 44 applied to a voice coil motor (VCM) 46which rotates an actuator arm 48 about a pivot in order to actuate thehead 20 radially over the disk surface 16 in a direction that reducesthe PES. The servo sectors 40 ₀-40 _(N) may comprise any suitable headposition information, such as a track address for coarse positioning andservo bursts for fine positioning. The servo bursts may comprise anysuitable pattern, such as an amplitude based servo pattern or a phasebased servo pattern.

During a write operation, a disturbance affecting the servo controlsystem that positions the head radially over the disk may cause the headto deviate from the center of the target data track resulting in anoff-track write. A disturbance that causes an off-track write maymanifest for any number of reasons, such as a physical shock to the diskdrive due to being bumped or dropped, a vibration affecting the diskdrive such as an audio signal, random electronic noise when reading theservo sectors, a grown defect in one or more servo sectors, etc. FIG. 3Ashows an example of an off-track write wherein the write element 52deviates from the center of a target data track 50A thereby overwritingpart of adjacent data track 50B. The off-track write shown in FIG. 3Amay span only part of a single data sector, or it may span multiple datasectors such as the data sectors between consecutive servo sectors, orit may span an entire data track. In any event, when attempting to readthe target data track 50A, the data recorded in the adjacent data track50B may interfere with the read signal (referred to as inter-trackinterference). If the target data track 50A is unrecoverable during aread operation, the prior art has suggested to perform a retry operationby positioning the write element 52 over the center of the adjacent datatrack 50B and erasing the adjacent data track 50B as shown in FIG. 3B.After erasing the adjacent data track 50B, the target data track 50A isread again with the inter-track interference attenuated, therebyimproving the chance of a successful read. However, positioning thewrite element 52 at the center and erasing the adjacent data track 50Bas illustrated in FIG. 3B may also erase part of the target data trackat the off-track write location, which may render the target datapermanently unrecoverable.

Accordingly, in one embodiment illustrated in FIG. 4A during a retryoperation the write element 52 is positioned offset from the center ofthe adjacent data track 50B away from the target data track 50A. Part ofthe adjacent data track 50B is then erased as illustrated in FIG. 4Bwithout erasing the target data at the off-track write location. Thecontrol circuitry 22 attempts to read the target data from the targetdata track, and if the target data is still unrecoverable, the writeelement 52 is positioned closer toward the target data track as shown inFIG. 4C and more of the adjacent data track 50B is erased as shown inFIG. 4D. If the target data is still unrecoverable, the processes isrepeated as shown in FIGS. 4E and 4F such that even more of the adjacentdata track 50B is erased without erasing the target data at theoff-track write location. As more of the adjacent data track 50B iserased, the inter-track interference is reduced until the target data atthe off-track write location may be successfully recovered.

FIG. 5 is a flow diagram according to an embodiment which extends on theflow diagram of FIG. 2B, wherein when a retry operation is needed (block24) data is read from the first adjacent data track 50B as well as fromthe next adjacent data track 50C and stored in a temporary location(e.g., in a different data track). In this manner, the data is savedbefore erasing part of the first adjacent data track 50B and the nextadjacent data track 50C at block 28. If the retry read of the targetdata track fails (block 56), the radial location of the head is adjustedtoward the target data track (block 58) and more of the first adjacentdata track is erased (block 60). The target data track is read again(block 62), and if the retry read fails again (block 64), the flowdiagram is repeated from block 58. If the retry read is successful atblock 64, the saved data is rewritten back to the first adjacent datatrack 50B as well as data in the next adjacent data track 50C (block66).

In one embodiment illustrated in FIG. 6, after erasing part of theadjacent data track at block 60 of FIG. 5 and when executing the retryread at block 62, the read element 68 may be positioned at a pluralityof different radial locations relative to the target data track and thetarget data track read at each radial location. This embodiment attemptsto find the radial location of the target data track where thesignal-to-noise ratio at the off-track write location is maximized,thereby improving the chances of successfully recovering the target dataat the off-track write location. Accordingly, this embodiment executesan outer loop wherein the radial offset for erasing the adjacent datatrack 50B is incrementally adjusted toward the target data track, and aninner loop wherein the radial offset for reading the target data track50A is adjusted in an attempt to recover the target data.

In one embodiment, the adjacent data track 50B is erased using asuitable erase pattern comprising a frequency range that is differentthan a frequency range spanned by the target data recorded in the targetdata track. FIG. 7 illustrates an example of this embodiment which showsan example frequency range 70 for the target data when using linearmagnetic recording (LMR) and an example frequency range 72 for thetarget data when using perpendicular magnetic recording (PMR). FIG. 7also illustrates an embodiment wherein the erase pattern comprise an ACpattern having a frequency that is higher than the frequency rangespanned by the target data. In one embodiment, erasing the adjacent datatrack 50B using an out-of-band erase pattern (e.g., a higher frequencyAC pattern) helps attenuate inter-track interference that may be causedby the erase pattern when reading the target data from the target datatrack.

The embodiment illustrated in FIGS. 4A-4F shows the adjacent data track50B on one side (right side) of the target data track being erased. Inanother embodiment, the adjacent data track on both sides of the targetdata track may be erased in a similar manner (by incrementally erasingfrom left to right and from right to left). This embodiment helpscompensate for off-track writes that may occur on either or both sidesof the target data track. Also in this embodiment, the radial offsets ofthe read element 68 as shown in FIG. 6 may include offsets toward bothof the left and right adjacent data tracks.

Any suitable control circuitry may be employed to implement the flowdiagrams in the above embodiments, such as any suitable integratedcircuit or circuits. For example, the control circuitry may beimplemented within a read channel integrated circuit, or in a componentseparate from the read channel, such as a disk controller, or certainoperations described above may be performed by a read channel and othersby a disk controller. In one embodiment, the read channel and diskcontroller are implemented as separate integrated circuits, and in analternative embodiment they are fabricated into a single integratedcircuit or system on a chip (SOC). In addition, the control circuitrymay include a suitable preamp circuit implemented as a separateintegrated circuit, integrated into the read channel or disk controllercircuit, or integrated into a SOC.

In one embodiment, the control circuitry comprises a microprocessorexecuting instructions, the instructions being operable to cause themicroprocessor to perform the flow diagrams described herein. Theinstructions may be stored in any computer-readable medium. In oneembodiment, they may be stored on a non-volatile semiconductor memoryexternal to the microprocessor, or integrated with the microprocessor ina SOC. In another embodiment, the instructions are stored on the diskand read into a volatile semiconductor memory when the disk drive ispowered on. In yet another embodiment, the control circuitry comprisessuitable logic circuitry, such as state machine circuitry.

While the above examples concern a disk drive, the various embodimentsare not limited to a disk drive and can be applied to other data storagedevices and systems, such as magnetic tape drives, solid state drives,hybrid drives, etc. In addition, some embodiments may include electronicdevices such as computing devices, data server devices, media contentstorage devices, etc. that comprise the storage media and/or controlcircuitry as described above.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and subcombinations are intended to fall withinthe scope of this disclosure. In addition, certain method, event orprocess blocks may be omitted in some implementations. The methods andprocesses described herein are also not limited to any particularsequence, and the blocks or states relating thereto can be performed inother sequences that are appropriate. For example, described tasks orevents may be performed in an order other than that specificallydisclosed, or multiple may be combined in a single block or state. Theexample tasks or events may be performed in serial, in parallel, or insome other manner. Tasks or events may be added to or removed from thedisclosed example embodiments. The example systems and componentsdescribed herein may be configured differently than described. Forexample, elements may be added to, removed from, or rearranged comparedto the disclosed example embodiments.

While certain example embodiments have been described, these embodimentshave been presented by way of example only, and are not intended tolimit the scope of the inventions disclosed herein. Thus, nothing in theforegoing description is intended to imply that any particular feature,characteristic, step, module, or block is necessary or indispensable.Indeed, the novel methods and systems described herein may be embodiedin a variety of other forms; furthermore, various omissions,substitutions and changes in the form of the methods and systemsdescribed herein may be made without departing from the spirit of theembodiments disclosed herein.

What is claimed is:
 1. A data storage device comprising: a diskcomprising a plurality of data tracks; a head actuated over the disk;and control circuitry configured to perform a retry operation for atarget data track by: positioning the head at a first radial locationand first erasing at least part of a first data track adjacent thetarget data track; after the first erasing, first reading the targetdata track to first recover target data recorded in the target datatrack; when the first recovery fails, positioning the head at a secondradial location and second erasing more of the first data track; andafter the second erasing, second reading the target data track to secondrecover the target data recorded in the target data track, wherein: thefirst erasing erases at least part of a second data track adjacent thefirst data track; and the first erasing erases more of the second datatrack than the first data track.
 2. The data storage device as recitedin claim 1, wherein the second radial location is closer to the targetdata track than the first radial location.
 3. The data storage device asrecited in claim 1, wherein: prior to the first erasing, the controlcircuitry is further configured to read first data from the first datatrack and read second data from the second data track; and after thesecond erasing, the control circuitry is further configured to write thefirst data to the first data track and write the second data to thesecond data track.
 4. The data storage device as recited in claim 1,wherein the first reading comprises positioning the head at a pluralityof radial locations relative to the target data track and reading thetarget data track at each radial location.
 5. The data storage device asrecited in claim 1, wherein: the target data comprises a first frequencyrange; and the first erasing comprises writing an erase pattern to thefirst data track, where the erase pattern comprises magnetic transitionshaving a second frequency range different than the first frequencyrange.
 6. The data storage device as recited in claim 5, wherein theerase pattern comprises an AC pattern comprising a frequency higher thanthe first frequency range.
 7. A method of operating a data storagedevice, the method comprising: performing a retry operation for a targetdata track of a disk by: positioning a head at a first radial locationand first erasing at least part of a first data track adjacent thetarget data track; after the first erasing, first reading the targetdata track to first recover target data recorded in the target datatrack; when the first recovery fails, positioning the head at a secondradial location and second erasing more of the first data track; andafter the second erasing, second reading the target data track to secondrecover the target data recorded in the target data track, wherein: thefirst erasing erases at least part of a second data track adjacent thefirst data track; and the first erasing erases more of the second datatrack than the first data track.
 8. The method as recited in claim 7,wherein the second radial location is closer to the target data trackthan the first radial location.
 9. The method as recited in claim 7,wherein: prior to the first erasing, further comprising reading firstdata from the first data track and read second data from the second datatrack; and after the second erasing, further comprising writing thefirst data to the first data track and writing the second data to thesecond data track.
 10. The method as recited in claim 7, wherein thefirst reading comprises positioning the head at a plurality of radiallocations relative to the target data track and reading the target datatrack at each radial location.
 11. The method as recited in claim 7,wherein: the target data comprises a first frequency range; and thefirst erasing comprises writing an erase pattern to the first datatrack, where the erase pattern comprises magnetic transitions having asecond frequency range different than the first frequency range.
 12. Themethod as recited in claim 11, wherein the erase pattern comprises an ACpattern comprising a frequency higher than the first frequency range.